Classes to Represent Unevaluated Language Objects

Description

The virtual class "language" and the specific classes that extend it represent unevaluated objects, as produced for example by the parser or by functions such as quote.

Usage

### each of these classes corresponds to an unevaluated object
### in the S language.
### The class name can appear in method signatures,
### and in a few other contexts (such as some calls to as()).

"("
"<-"
"call"
"for"
"if"
"repeat"
"while"
"name"
"{"

### Each of the classes above extends the virtual class
"language"

Objects from the Class

"language" is a virtual class; no objects may be created from it.

Objects from the other classes can be generated by a call to new(Class, ...), where Class is the quoted class name, and the ... arguments are either empty or a single object that is from this class (or an extension).

Methods

coerce

signature(from = "ANY", to = "call"). A method exists for as(object, "call"), calling as.call().

Examples

showClass("language")

is( quote(sin(x)) ) # "call"  "language"

(ff <- new("if"))  ; is(ff) # "if" "language"
(ff <- new("for")) ; is(ff) # "for" "language"